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ASTM E1949-03

(Test Method)

Standard Test Method for Ambient Temperature Fatigue Life of Metallic Bonded Resistance Strain Gages

Standard Test Method for Ambient Temperature Fatigue Life of Metallic Bonded Resistance Strain Gages

SIGNIFICANCE AND USE
Strain gages are the most widely used devices for measuring strains and for evaluating stresses in structures. In many applications there are often cyclic loads which can cause strain gage failure. Performance parameters of strain gages are affected by both the materials from which they are made and their geometric design.
The determination of most strain gage parameters requires mechanical testing that is destructive. Since gages tested for fatigue life cannot be used again, it is necessary to treat data statistically. In general, longer and wider gages with lower resistances will have greater fatigue life. Optional additions to gages (integral leads are an example) will often reduce fatigue life.
To be used, strain gages must be bonded to a structure. Good results, particularly in a fatigue environment, depend heavily on the materials used to clean the bonding surface, to bond the gage, and to provide a protective coating. Skill of the installer is another major factor in success. Finally, instrumentation systems must be carefully selected and calibrated to ensure that they do not unduly degrade the performance of the gages.
This test method encompasses only fully reversed strain cycles.
Fatigue failure of a strain gage may not involve visible cracking or fracture of the gage, but merely sufficient zero shift to compromise the accuracy of the gage output for static strain components.
SCOPE
1.1 This test method covers a uniform procedure for the determination of strain gage fatigue life at ambient temperature. A suggested testing equipment design is included.
1.2 This test method does not apply to force transducers or extensometers that use bonded resistance strain gages as sensing elements.
1.3 Strain gages are part of a complex system that includes structure, adhesive, gage, leadwires, instrumentation, and (often) environmental protection. As a result, many things affect the performance of strain gages, including user technique. A further complication is that strain gages, once installed, normally cannot be reinstalled in another location. Therefore, it is not possible to calibrate individual strain gages; performance characteristics are normally presented on a statistical basis.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to its use.

General Information

Status
Historical
Publication Date
09-Sep-2003
ICS
19.060 - Mechanical testing
Technical Committee
E28 - Mechanical Testing
Drafting Committee
E28.01 - Calibration of Mechanical Testing Machines and Apparatus
Current Stage
Ref Project

Relations

Replaces
ASTM E1949-02 - Standard Test Method for Ambient Temperature Fatigue Life of Metallic Bonded Resistance Strain Gages
Effective Date
10-Sep-2003
Replaced By
ASTM E1949-03(2009) - Standard Test Method for Ambient Temperature Fatigue Life of Metallic Bonded Resistance Strain Gages
Effective Date
01-Apr-2009

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ASTM E1949-03 - Standard Test Method for Ambient Temperature Fatigue Life of Metallic Bonded Resistance Strain GagesASTM E1949-03 - Standard Test Method for Ambient Temperature Fatigue Life of Metallic Bonded Resistance Strain Gages
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ASTM E1949-03 - Standard Test Method for Ambient Temperature Fatigue Life of Metallic Bonded Resistance Strain Gages
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Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation:E1949–03
Standard Test Method for
Ambient Temperature Fatigue Life of Metallic Bonded
1
Resistance Strain Gages
This standard is issued under the fixed designation E 1949; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope performance, whether due to excessive zero shift or other
detectable failure mode (see Section 9.6).
1.1 This test method covers a uniform procedure for the
determination of strain gage fatigue life at ambient tempera-
4. Significance and Use
ture. A suggested testing equipment design is included.
4.1 Strain gages are the most widely used devices for
1.2 This test method does not apply to force transducers or
measuring strains and for evaluating stresses in structures. In
extensometers that use bonded resistance strain gages as
many applications there are often cyclic loads which can cause
sensing elements.
strain gage failure. Performance parameters of strain gages are
1.3 Strain gages are part of a complex system that includes
affected by both the materials from which they are made and
structure, adhesive, gage, leadwires, instrumentation, and (of-
their geometric design.
ten) environmental protection. As a result, many things affect
4.2 The determination of most strain gage parameters re-
the performance of strain gages, including user technique. A
quires mechanical testing that is destructive. Since gages tested
further complication is that strain gages, once installed, nor-
forfatiguelifecannotbeusedagain,itisnecessarytotreatdata
mally cannot be reinstalled in another location. Therefore, it is
statistically. In general, longer and wider gages with lower
not possible to calibrate individual strain gages; performance
resistances will have greater fatigue life. Optional additions to
characteristics are normally presented on a statistical basis.
gages (integral leads are an example) will often reduce fatigue
1.4 This standard does not purport to address all of the
life.
safety concerns, if any, associated with its use. It is the
4.3 To be used, strain gages must be bonded to a structure.
responsibility of the user of this standard to establish appro-
Good results, particularly in a fatigue environment, depend
priate safety and health practices and determine the applica-
heavily on the materials used to clean the bonding surface, to
bility of regulatory limitations prior to its use.
bond the gage, and to provide a protective coating. Skill of the
2. Referenced Documents installer is another major factor in success. Finally, instrumen-
2
tation systems must be carefully selected and calibrated to
2.1 ASTM Standards:
ensure that they do not unduly degrade the performance of the
E 1237 Guide for Installing Bonded Resistance Strain
gages.
Gages
4.4 This test method encompasses only fully reversed strain
3. Terminology
cycles.
4.5 Fatigue failure of a strain gage may not involve visible
3.1 strain gage fatigue life, n—the number of fully reversed
cracking or fracture of the gage, but merely sufficient zero shift
strain cycles corresponding to the onset of degraded gage
to compromise the accuracy of the gage output for static strain
components.
1
This test method is under the jurisdiction of ASTM Committee E28 on 5. Interferences
Mechanical Testing and is the direct responsibility of Subcommittee E28.01 on
5.1 In order to ensure that strain gage test data are within a
Calibration of Mechanical Testing Machines and Apparatus. Current edition
defined accuracy, the gages must be properly bonded and
approvedNov.15,2005.PublishedOctober2003.Originallyapprovedin1998.Last
previous edition approved in 2002 as E 1949 – 02.
protected with acceptable materials. Aids in the strain gage
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
installation and verification thereof can be found in Guide
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
E 1237. It is important to note that good performance in cyclic
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. applications requires the best installations possible.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
1

---------------------- Page: 1 ----------------------
E1949–03
6. Hazards beams and crazing of plastic specimens are examples of beam
failures that will produce faulty, misleadingly low, strain gage
6.1 Warning—In the specimen surface cleaning, gage bond-
fatigue life.
ing, and protection steps of strain gage installations, hazardous
7.2.1.1 Beam specimens must b
...

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SIGNIFICANCE AND USE
4.1 Strain gages are the most widely used devices for measuring strains and for evaluating stresses in structures. In many applications there are often cyclic loads that can cause strain gage failure. Performance characteristics of strain gages are affected by both the materials from which they are made and their geometric design.  
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1.1 This test method covers a uniform procedure for the determination of strain gage fatigue life at ambient temperature. A suggested testing equipment design is included.  
1.2 This test method does not apply to force transducers or extensometers that use metallic bonded resistance strain gages as sensing elements.  
1.3 Strain gages are part of a complex system that includes structure, adhesive, strain gage, lead wires, instrumentation, and (often) environmental protection. As a result, many things affect the performance of strain gages, including user technique. A further complication is that strain gages, once installed, normally cannot be reinstalled in another location. Therefore, it is not possible to calibrate individual strain gages; performance characteristics are normally presented on a statistical basis.  
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4.1 Methods and procedures used in installing bonded resistance strain gages can have significant effects upon the performance of those sensors. Optimum and reproducible detection of surface deformation requires appropriate and consistent strain gage and bonding technique selection, surface preparation, procedures for gage installation and adhesive use, lead wire connection, validation of operation, and protective coating application.
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1.1 This guide provides guidelines for installing bonded resistance strain gages. It is not intended to be used for bulk or diffused semiconductor gages. This guide pertains only to adhesively bonded strain gages.  
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
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Standard Test Methods for Performance Characteristics of Metallic Bonded Resistance Strain Gages

SIGNIFICANCE AND USE
4.1 Strain gages are the most widely used devices for the determination of materials, properties and for analyzing stresses in structures. However, performance characteristics of strain gages are affected by both the materials from which they are made and their geometric design. These test methods detail the minimum information that must accompany strain gages if they are to be used with acceptable accuracy of measurement.  
4.2 Most performance characteristics of strain gages require mechanical testing that is destructive. Since test strain gages cannot be used again, it is necessary to treat data statistically and then apply values to the remaining population from the same lot or batch. Failure to acknowledge the resulting uncertainties can have serious repercussions. Resistance measurement is non-destructive and can be made for each strain gage.  
4.3 Properly designed and manufactured strain gages, whose performance characteristics have been accurately determined and with appropriate uncertainties applied, represent powerful measurement tools. They can determine small dimensional changes in structures with excellent accuracy, far beyond that of other known devices. It is important to recognize, however, that individual strain gages cannot be calibrated. If calibration and traceability to a standard are required, strain gages should not be employed.  
4.4 To be used, strain gages must be bonded to a structure. Good results depend heavily on the materials used to clean the bonding surface, to bond the strain gage, and to provide a protective coating. Skill of the installer is another major factor in success. Finally, instrumentation systems must be carefully designed to assure that they do not unduly degrade the performance of the strain gages. In many cases, it is impossible to achieve this goal. If so, allowance must be made when considering accuracy of data. Test conditions can, in some instances, be so severe that error signals from strain gage systems far ...
SCOPE
1.1 The purpose of these test methods are to provide uniform test methods for the determination of strain gage performance characteristics. Suggested testing equipment designs are included.  
1.2 Test Methods E251 describes methods and procedures for determining five strain gage performance characteristics:    
Section  
Part I—General Requirements  
7  
Part II—Resistance at a Reference Temperature  
8  
Part III—Gage Factor at a Reference Temperature  
9  
Part IV—Temperature Coefficient of Gage Factor  
10  
Part V—Transverse Sensitivity  
11  
Part VI—Thermal Output  
12  
1.3 Strain gages are very sensitive devices with essentially infinite resolution. Their response to strain, however, is low and great care must be exercised in their use. The performance characteristics identified by these test methods must be known to an acceptable accuracy to obtain meaningful results in field applications.  
1.3.1 Strain gage resistance is used to balance instrumentation circuits and to provide a reference value for measurements since all data are related to a change in the strain gage resistance from a known reference value.  
1.3.2 Gage factor is the transfer function of a strain gage. It relates resistance change in the strain gage and strain to which it is subjected. Accuracy of strain gage data can be no better than the accuracy of the gage factor.  
1.3.3 Changes in gage factor as temperature varies also affect accuracy although to a much lesser degree since variations are usually small.  
1.3.4 Transverse sensitivity is a measure of the strain gage's response to strains perpendicular to its measurement axis. Although transverse sensitivity is usually much less than 10 % of the gage factor, large errors can occur if the value is not known with reasonable precision.  
1.3.5 Thermal output is the response of a strain gage to temperature changes. Thermal output is an additive (not multiplica...

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Standard Practice for Verification of Testing Frame and Specimen Alignment Under Tensile and Compressive Axial Force Application

SIGNIFICANCE AND USE
4.1 It has been shown that bending stresses that inadvertently occur due to misalignment between the applied force and the specimen axes during the application of tensile and compressive forces can affect the test results. In recognition of this effect, some test methods include a statement limiting the misalignment that is permitted. The purpose of this practice is to provide a reference for test methods and practices that require the application of tensile or compressive forces under conditions where alignment is important. The objective is to implement the use of common terminology and methods for verification of alignment of testing machines, associated components and test specimens.  
4.2 Alignment verification intervals when required are specified in the methods or practices that require the alignment verification. Certain types of testing can provide an indication of the current alignment condition of a testing frame with each specimen tested. If a test method requires alignment verification, the frequency of the alignment verification should capture all the considerations that is, time interval, changes to the testing frame and when applicable, current indicators of the alignment condition through test results.  
4.3 Whether or not to improve axiality should be a matter of negotiation between the interested parties.
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